Osteoporosis on its own does not cause symptoms. Unless it's caused a bone fracture, it's not a painful condition, nor is it a type of arthritis.

Understanding bone structure

Our bones carry out various jobs in the body. Not only do they provide a solid frame to carry the weight of the tissues and protect some organs, but they are also the sites of manufacture of most of the components of blood (the bone marrow).

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As a result they need to be both strong and yet contain space for the bone marrow.

Bone has a complex structure that achieves the maximum amount of strength for the least amount of weight.

If you take a typical bone, such as the femur (upper leg bone), and cut it across – you will see there's an outer shell of hard bone. In the middle space it has a honeycomb structure (that helps to keep the bone light) through which is mingled the bone marrow.

Bone is made up mostly of collagen fibres, upon which are laid down crystals made from calcium and phosphate that give bone its ability to withstand compression and bending forces. These give the bone a structure like scaffolding with fibres forming strong cross-struts.

But bone is a living tissue and it can increase its thickness in areas subjected to repeated heavy loads (this is called remodelling) and repair itself when broken.

Cells that repair and dissolve bone

If you looked at bone under a microscope, you'd see two types of specialised cells scattered throughout:

cells that continually make new bone, called osteoblasts

cells that continuously dissolve bone into its component materials, called osteoclasts.

Bone is therefore not a static tissue, but is always on the go. The actions of bone manufacture and disassembly are usually exactly balanced.

How bone repairs itself

When increased loads are repeatedly put upon a bone, the osteoblasts become more active, laying down more bone and increasing the strength of the region.

When a bone fractures, osteoblasts go into overdrive around the fracture site, laying down more collagen fibres and minerals on top to strengthen them.

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How does osteoporosis affect bone?

Osteoporosis is a complex disease with a number of different factors involved in its development, which may cause a failure to build bone in young adult life, or a progressive bone loss later on.

Poor diet and lack of exercise earlier in life, as well as genetic factors, can mean that a person doesn't build their bones properly and never reaches the optimum peak level of bone mass and strength that should be reached in our third decade.

In osteoporosis that occurs after the menopause, there is excessive activity of the osteoclasts which dissolve a bit more bone than is replaced, resulting in weaker bones.

But the bone loss which generally accompanies aging is due to a progressive decline in the supply of osteoblasts compared to demand.

Fractures in bone affected by osteoporosis are most likely in areas where there is a greater percentage of the honeycomb type of bone, which is less able to take the shock of a fall:

in the wrist

in the femur close to the hip joint (called the 'neck' of the femur)

in the vertebrae of the lower spine.

Hip and wrist fractures usually result from falls, whereas fractures of the spine tend to occur spontaneously when a weakened vertebra eventually crumples under the stress of supporting the body's weight.

The scale of the problem

One in three women and 1 in 12 men over the age of 50 will suffer a fracture of the hip, wrist or spine as a result of osteoporosis.

In total, osteoporosis causes 310,000 fractures in the UK every year. The estimated cost of treating these fractures runs into several billion pounds each year if you include the social care that many need afterwards because of permanent disability.

But the cost to the individual can be higher.

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Bone fractures can cause considerable pain and disability.

For example, 10 per cent of people who suffer a fractured hip are dead within a month, rising to 30 per cent by one year.

Another 30 per cent will lose their independence and require long-term care, while 30 per cent more remain independent but don't manage to return to their previous level of functioning. Only a small percent return to normal.

Vertebral fractures can be a source of chronic pain and other complications

Detecting osteoporosis

The majority of people who suffer a fracture from osteoporosis are not known to have the condition prior to breaking their bone.

Osteoporosis is an under-recognised condition, which is partly because an organised approach to detecting it, such as a national screening programme, has not yet been developed in the UK.

As a result, people at high risk of getting a fracture may not be offered appropriate advice or treatment to reduce their risk.

There are wide variations throughout the UK in the quality and quantity of effort put into detecting and treating osteoporosis.

There are further divisions in the quality of care delivered to people from different social groups. In a recent study in Glasgow, people from the most deprived areas were eight times less likely to be referred for tests to detect osteoporosis than those from affluent areas.

However, the government has recognised the deficiencies that exist in osteoporosis management nationally.

Since 2012 GPs have been given financial incentives for diagnosing and treating osteoporosis in their patients, and for keeping a register of those with fragility fractures to monitor their treatment. This should lead to better access to diagnostic scans for osteoporosis and better use of treatments.

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More funding is also slowly coming through to fund bone scanning machines to help diagnosis as well as specialists in osteoporosis.

If you aged 50 or over and have broken a hip, wrist or vertebrae simply after a minor fall or event (ie not in a major road crash or similar accident) you should talk to your GP about osteoporosis.

Those aged less than 74 should be sent for a DEXA scan to confirm the diagnosis. A scan is not necessary for those over 74, who are simply advised to consider taking bone-protection drugs (as a degree of age-related osteoporosis will be assumed).

What's classified as 'abnormally weak'?

It is normal for bone to get a bit weaker each year after the age of about 30, when our bones are at their maximum strength. Men tend to have greater bone mass than women of the same age.

For a few years after the menopause, women experience an increased rate of bone loss. This is secondary to the drop in oestrogen that is part of the hormone change of menopause – oestrogen has a protective effect upon bone strength.

Defining when bones are abnormally weak has to take account of what is normal for the two sexes and the different age groups.

Modern bone scanning devices (see below) can measure the density of bones and have allowed doctors to set a range for normal bone strength. Osteoporosis can therefore be diagnosed if a person's bone density measurement is significantly low compared to these standards.

Low impact 'fragility' fractures

A person is also deemed to have osteoporosis if they have suffered a fracture too easily, ie a 'low impact', 'fragility' or 'osteoporotic' fracture.

A low trauma fracture is:

one that occurs from a fall from standing height or less

a fracture of the hip, wrist or forearm.

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It's more difficult to categorise vertebral fractures because they occur out of the blue and are not related to falls – sometimes they are not even accompanied by much pain.

However, the sudden onset of back pain should suggest there has been a collapsed vertebra, possibly due to osteoporosis.

Identifying people who have osteoporosis after they have suffered a fracture means they can be offered preventative treatments which will reduce the chance of another fracture later.

Causes of osteoporosis

Various factors are known to increase the rate at which bone loss occurs.

These can be divided into three groups:

factors you can do nothing about

things you can change

causes related to other medical conditions or drug therapy.

Listed below are some of the main conditions that can lead to osteoporosis.

Unchangeable causes of increased bone loss

Increasing age.

Family history of osteoporosis (genetics account for as much as 80 per cent of the natural variation in bone mass, and so plays an important part in risk).

Protein deficiency or any condition which causes malabsorption of food such as Crohn's or coeliac Disease.

Diagnosing osteoporosis

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The best test to diagnose osteoporosis is a scan to determine the density of the bones, the bone mineral density (BMD) test.

BMD tends to vary between different sites in the body, so a clinic will usually use the same reference point in the skeleton to allow better comparison between different people. The hip, forearm, heel bone or spine are all used, but exactly which varies according to local procedure.

DEXA scan

There are several ways in which a bone scan can be done, but the best is the 'DEXA' scan. DEXA is short for dual-energy X-ray absorptiometry.

As the name implies, a DEXA scan uses X-rays to determine the density of bone. DEXA scans usually check one of the following: the anteroposterior (AP – ie from front to back) spine, lateral spine, proximal femur, total body, forearm, heel (calcaneus).

Similar techniques may be used on specific parts of the body, such as quantitative CT scanning on the spine, or single photon absorptiometry (SPA) on the forearm to measure BMD.

Ultrasound

Ultrasound of the heel bone is another common technique for determining the quality and structure of the bones. It uses cheaper equipment, but it's not yet clear if it is as accurate or reliable as DEXA scanning, and is not accepted as a reliable way to diagnose osteoporosis or guide treatment.

X-rays

Ordinary X-rays are not reliable as a tool for diagnosing osteoporosis. It can be possible to suspect from a standard X-ray that the person has less bone mass than normal, because the bone outline on the film might appear fainter.

However, the same appearance will show if the exposure of the film is slightly too high. Conversely, if the film is slightly underexposed, the bones will look normally dense.

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As much as 30 per cent of bone mass needs to be lost before it shows up on ordinary X-rays.

Who can have a DEXA scan?

There are not enough DEXA scanners in the UK to make the test freely available, so some form of vetting procedure is used to ensure that those most at need are being scanned.

The details of these criteria vary across the UK, but could looklike the list below, in which the presence of any one factor would justify a DEXA scan.

A woman over 50 who has had a low trauma fracture.

Anyone taking an oral steroid, eg prednisolone 5mg daily, or greater, for three months or more.

A woman under 45 who has had an early menopause or removal of the ovaries.

A man with a high alcohol consumption of more than 50 units of alcohol weekly.

A woman who is around the menopause with any two of the following:

a body mass index (BMI) less than 21

a history in her mother of a hip fracture below 80 years of age

who smokes

who drinks more than 35 units of alcohol weekly (see below).

FRAX scores

Many fragility fractures occur in people with bone density values (BMDs) above the level defined as normal.

The risk of a fractures now can be better predicted by adding clinical risk factors that contribute to fracture risk independently of BMD.

These include factors such as weight, alcohol and smoking habits, treatment with steroids and a family history of hip fracture.

There is now a WHO fracture risk assessment tool (FRAX) that can be easily used to calculate the ten-year probability of a major osteoporotic fracture (with or without a BMD result).

Another tool is also used in the UK called the QFracture score.

Prevention and treatment

There are some general measures that people can take to prevent and treat osteoporosis including changing their diet and modifying their lifestyle and attitude to exercise, as well as taking supplements or treatment prescribed by a doctor.

Thinness

People who are unusually thin are more likely to develop osteoporosis, and the way to define 'thinness' is to measure your body mass index (BMI).

People with a BMI of 21 or less have a higher rate of bone loss than those who are heavier, and obese people have lower rates of bone loss than those who are ideal weight.

It is not known if a thin person who deliberately puts on a lot of weight will reduce their subsequent fracture risk.

Alcohol

Historically, the recommended maximum consumption of alcohol per week, in terms of general health, has been 14 units for women and 21 units for men.

More recently this has been changed to focus on daily limits because the harm associated with binge drinking has been recognised. So recommended limits are now 2-3 units of alcohol a day for women and 3 to 4 for men.

High levels of alcohol intake (over 50 units per week in men or 35 units in women) are associated with osteoporosis, as well as the other serious health risks that accompany alcoholism.

It is possible that lower levels of alcohol consumption than this could still damage bone and be associated with problems such as raised blood pressure or diabetes.

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